The present invention relates generally to annuloplasty prostheses and methods for repair of heart valves. More particularly, it relates to annuloplasty rings, and related instruments and procedures, for surgically reconstructing a valve annulus of a patient's heart, for example a mitral valve annulus.
Annuloplasty prostheses, generally categorized as either annuloplasty rings or annuloplasty bands, are employed in conjunction with valvular reconstructive surgery to assist in the correction of heart valve defects such as stenosis and valvular insufficiency. There are two atrio-ventricular valves in the heart. The mitral valve is located on the left side of the heart, and the tricuspid valve is located on the right side. Anatomically speaking, each valve type forms or defines a valve annulus and valve leaflets. To this end, the mitral and tricuspid valves differ significantly in anatomy. For example, the annulus of the mitral valve is somewhat “D” shaped, whereas the annulus of the tricuspid valve is more nearly circular.
Both valves can be subjected to or incur damage that requires the valve in question be repaired or replaced. The effects of valvular dysfunction vary. For example, mitral regurgitation, a complication of end-stage cardiomyopathy, has more severe physiological consequences to the patient as compared to tricuspid valve regurgitation. Regardless, many of the defects are associated with dilatation of the valve annulus. This dilatation not only prevents competence of the valve, but also results in distortion of the normal shape of the valve orifice. Remodeling of the annulus is therefore central to most reconstructive procedures on the mitral valve. In this regard, clinical experience has shown that repair of the valve, when technically possible, produces better long-term results as compared to valve replacement.
Many procedures have been described to correct the pathology of the valve leaflets and their associated chordae tendinae and papillary muscles. For example, with respect to the mitral valve, it is a bicuspid valve having a large posterior leaflet that coapts or meets with a smaller anterior leaflet. The part of the mitral valve annulus that is attached to the anterior leaflet is called the anterior aspect, while the part attached to the posterior leaflet is called the posterior aspect. There are two fibrous trigones that nearly straddle the anterior aspect. With this in mind, in mitral repairs, it is considered important to preserve the normal distance between the two trigones. A significant surgical diminution of the inter-trigonal distance may cause left ventricular outflow obstruction. Thus, it is desirable to maintain the natural inter-trigonal distance during and following mitral valve repair surgery.
Consequently, when a mitral valve is repaired surgically, the result is generally a reduction of the size of the posterior aspect of the mitral valve annulus. As part of a typical mitral valve repair, an annulus is diminished (i.e., constricted) so that the leaflets may coapt correctly upon closing of the valve, or an annulus or segment thereof (e.g., anterior or posterior aspect) is stabilized to prevent post-operative dilatation from occurring, either as frequently achieved by implantation of a prosthetic ring or band in a supra annular position. The purpose of a ring or band is to restrict and/or support an annulus to correct and/or prevent valvular insufficiency. However, it is important not to overly restrict an annulus as an unacceptable valvular stenosis may result. In tricuspid valve repair, constriction of an annulus usually takes place by positioning a band partially about the posterior leaflet segment and a small portion of the adjacent anterior leaflet segment. The septal leaflet segment is not usually required to be shortened.
As described above, both annuloplasty rings and annuloplasty bands are available for repair of an atrio-ventricular valve. Examples of annuloplasty rings are shown in U.S. Pat. Nos. 5,306,296; 5,669,919; 5,716,397; and 6,159,240, the teachings of which are incorporated herein by reference. In general terms, annuloplasty rings completely encompass both the anterior and posterior aspects of a valve annulus, and have either a rigid (or semi-rigid) design, or a flexible design. Annuloplasty bands, on the other hand, are specifically designed to primarily encompass only a portion of the valve annulus. With the rigid or semi-rigid configuration, an annuloplasty ring serves to remodel the dysfunctional valve annulus to a desired shape such as that which would mimic the normal systolic shape of the valve. In this regard, and relative to the mitral valve, recent studies have identified that the healthy mitral valve annulus has a natural saddle shape that becomes exaggerated in systole. Efforts have been made to provide a rigid annuloplasty ring that more closely mimics this saddle shape, for example as shown in U.S. Pat. No. 6,858,039 and U.S. Publication No. 2003/0093148, the teachings of which are incorporated herein by reference. While viable, this remodeling/rigid annulus support may overtly restrict natural movement of the mitral valve annulus when functioning during diastole and systole, especially in the mitral valve anterior aspect as suggested by Parrish, L. M., et al., The Dynamic Anterior Mitral Annulus, (Annals. of Thoracic Surgery 2004; 78:1248-55).
While the suggested saddle-shaped annuloplasty rings may assist in achieving valve annulus remodeling that more closely mimics the natural shape of a healthy valve annulus, other concerns may arise. For example, it is difficult to accurately estimate whether any saddle-shaped annuloplasty ring is of an appropriate size for the valve to be repaired. In particular, conventional annuloplasty ring implantation procedures entail initially performing a cardiac bypass operation, followed by use of a sizing instrument to estimate a size of the valve annulus in question. In general terms, a surgeon will have available to him or her a number of differently sized annuloplasty rings, along with a number of sizer bodies each having a size and shape corresponding with a respective one of the annuloplasty rings on hand. Because a heart is flaccid during cardiac bypass, a valve annulus in question will be in a diastolic shape (e.g., essentially non-saddled or flat). In contrast, a saddled annuloplasty ring, and thus a corresponding sizer body, reflects the systolic end shape of the valve annulus. Thus, comparing a saddle-shaped sizer body with a valve annulus in a relatively flat, diastolic end state may not provide an accurate sizing estimate. In addition, the suggested saddle-shaped mitral valve annuloplasty rings may create leaflet tethering in dilated cardiomyopathy and ischemic mitral regurgitation applications. Further, where an annuloplasty ring is shaped to rigidly or semi-rigidly remodel the valve annulus to the saddle shape associated with the systolic end state, the existing leaflets may be distorted; further, the annuloplasty ring is subjected to significant forces as the valve transitions between the systolic and diastolic states, potentially leading to long-term annuloplasty ring degradation from fatigue, such as fracturing or dehiscence.
In contrast to annuloplasty rings, annuloplasty bands are specifically designed to primarily encompass only a portion of a valve annulus. For example, a mitral valve annuloplasty band is typically configured to encompass only the posterior aspect of a mitral valve annulus, thus promoting natural movement of the anterior aspect. Examples of annuloplasty bands are shown in U.S. Pat. Nos. 5,824,066 and 6,786,924, and PCT International Patent Publication No. WO00/74603, the teachings of which are incorporated herein by reference. While quite viable, annuloplasty bands may present other concerns. First, the profile (e.g., thickness) of some annuloplasty bands may theoretically be sufficiently large so as to restrict or disturb blood flow. Also, an annuloplasty band may not provide sufficient restriction to possible dilatation of a valve annulus aspect(s) otherwise not encompassed by the band (e.g., the anterior aspect of the mitral valve annulus). Ischemic mitral regurgitation and dilated cardiomyopathy are two examples of clinical applications of these phenomena that might otherwise indicate a potential for anterior dilatation.
In light of the above, a need exists for improved annuloplasty ring designs, and related surgical instruments and techniques that more accurately reflect both the shape and functioning of a healthy valve annulus, such as a mitral valve annulus.